Pick-up device for electrical musical instruments



June 1, 1938. A. F. KNOBLAUGH 9,

PICK-UP DEVICE FOR ELECTRICAL MUSICAL INSTRUMENTS Fi led Dec. 9,1935 2sheets-sheet 1 y- Ftyz ////Zn.]3/Z /7.

[NVEJVTQR ATTX June 7, 1938. A. F. KNOBLAUGH PICK-UP DEVICE FORELECTRICAL MUSICAL INSTRUMENTS Filed Dec. 9, 1955 2 Shgets-Sheet 2 z f x#m f; M .J u/ w mm 7 x M MM f .g M F 8 p Patented June 7, 1938 UNITEDSTATES PATENT OFFICE PICK-UP DEVICE FOR ELECTRICAL MUSI- CAL INSTRUMENTSArmand F. Knoblaugh, Cincinnati, Ohio, assignor to The Baldwin Company}Cincinnati, Ohio Application December 9, 1935, Serial No. 53,589

5 Claims.

terial, the translation of the motion of the vi- The electromotiveforces generated in an electromagnetic pick-up device of an electricalmusical instrument employing tuned vibrators have been found to be verysmall. In order to hear these induced electrical vibrations reproducedas musical tones from a loudspeaker of conventional type, some form ofamplification involving thermionic-vac'uum tubes is necessary.

In general, the supply of electrical power for an amplifier can befurnished most economically and conveniently when a commercial source ofsupply is used; batteries require frequent inspection and replacementand there are obvious disadvantages in the use of other types of purelylocal power sources.

In an electrical musical instrument for use in a home, there are oftenadvantages in placing the amplifier and loudspeaker in the case orcabinet of the instrument groper. When this is done, however, theamplifier and speaker will have been placed rather near the pick-updevice. Since commercial electric mains usually supply alternatingcurrent, the pick-up device will be exposed to stray alternatingelectric and magnetic fields, due mainly to the leakage flux from theamplifier power transformer, to a lesser degree to flux from the chokecoils of the amplifier filter system and from the loudspeaker field coil(in which structures .there are usually some residual alter: natingcurrents flowing) and from any other sources in the vicinity. Thesestray fields act upon the pick-up device to produce an alternatingelectromotive force, which is amplified and reproduced as anobjectionable hum.

The eifect'of the stray electric fields can be reduced satisfactorily byan electrostatic shield enclosing the pick-up structure. Magneticshielding, however, has not been found to be so eifec tive, and is notconvenient to employ in my invention, as will be obvious in my futuredescription. Therefore, another principle must be used to minimize theeifect of the stray magnetic fields; theemployment of this principle is.the main object of this invention. This and other objects which will beevident to those reading this specification,

I shall now explain and shall describe my invention in detail.

In the drawings which form a part hereof:

Fig. l is a side view of the form on and in which are placed theelements of the pick-up device to be described.

Fig. 2 is a plan view of the assembled structure,

showing in proximity the tuned vibrators, exem- I plarily indicated hereas tuned strings.

Fig. 3 is a side view, showing the adjacent. strings, in section.

\ Fig. 4 is a cross-section taken on A-B of Fig. 2

Figs. 5- and 6 are wiring diagrams, showing two schematic arrangementsfor connecting the device to an amplifier.

Fig. 7 is a partial wiring diagram of anamplifier.

In making a pick-up device in accordance with my invention, holders l, 2and 3, of insulating material and having in each a central lengthwiseslot, are properly spaced on two insulating strips 4 and 5, inserted andspaced apart in the slots of holders 1, 2 and 3. At the ends of thestrips 4 and 5 are inserted half-round pieces 6 and I, thus completingsmooth forming surfaces.

In the space between the strips 4 and 5 and end pieces 6 and 1, two setsof silicon steel 1aminations 8 and 9 are" fit tightly and spaced aparttherein by an insulating, non-magnetic piece W.

In the space between holders; and 2, on the smooth surface formed bystrips 4 and 5 and halfround pieces 6 and I, and around the laminated,steel core 8, is placed a coil H of fine, insulated copper wire. In asimilar manner a coil H of the same kind of wire is placed in the spacebetween holders 2 and 3 on the surface formed by strips 4 and 5 andhalf-round pieces 5 and 'l, and

around the laminated steel core 9. The end wires 13 and ll of the coilII and the end,wires l5 and iii of the coil I2 may be convenientlyattached to terminal posts set in an insulating plate,

the pitches of a musical scale and can be set in motion by the impact ofhammers as is done in instruments of the piano type, or can be excitedin any other well known manner.

The motions of the magnetized strings (and strings composed of the highcarbon steel used for piano wire will retain their magnetism for a considerable length of time) and the consequent motions of the flux fromthe magnetic poles on the strings, cyclically toward and away from thepickup device, induce corresponding electromotive forces in the coils Hand I2 by electromagnetic induction, which can be amplified andreproduced as musical tones. It is to be noted particularly, in thisrespect, that essentially all of the induced electromotive forces aregenerated in the coil i2 which is nearer to the strings I'd (see Figs. 3and f1) and that very little of the electromotive forces are generatedin the farther coil Ii, because of its greater distance from the stringsand the magnetic isolation effected by the nonmagnetic piece l0.

The principal object of my invention is the elimination of effectscaused by stray magnetic accomplish by efiecting external to theamplifier the connection between the first choke coil 21 and terminalsof wires I4 and i 6, the terminals of wires i3 and I5 becoming theoutput terminals of the device. The induction of electromotive forces bystray magnetic fields into coil I2 is then counterbalanced, part bypart, by the induction of equal and opposite electromotive forces intocoil I l, with the result that any reproduced extraneous noises, such ashum, are essentially eliminated.

The functioning of the device as a pick-up structure is not affected,however, as has been ex:

plained in the preceding paragraph. It is to be,

noted, in' this respect, that in practice, the crosssectional dimensionsof the device (such as the dimensions of Fig. 4) would be small ascompared with the distance from it to any source of stray I magneticflux, but that these cross-sectional dimensions are large as comparedwith the distance from the strings to the device. The main object of myinvention can be also accomplished by connecting the two coils in parallel in an opposite sense. This can be done by joining the terminals ofwires l3 and ii to i'orm one output terminal and by joining theterminals of wires l4 and Hi to form the other output terminal of thedevice. I

In Fig. 7 is shown a partial wiring diagram of an amplifier. As theprinciples oi operation 01 this amplifier are well known to thoseacquainted with the art and will be understood on examining thisspecification, I shall not describe it in complete detail, except tonote that it has input terminals I I and I9, output terminals 20 and 2|,8.

rectifier-filter system 22, terminals 22 and 24 for supplying rectifiedcurrent to a field coil 28 of a loudspeaker, and a terminal 26 which canbe used (in conjunction with a return terminal such as I!) for supplyingrectified current for magnetically charging the strings H, with the useof the device of this invention.

As it is necessary to supply current for magnetic charging only 'forshort periods of time, I have arranged that this current be furnished bydiverting, when necessary, a part of the output current or therectifier-filter system 22. This I the second choke coil 28, of thesystem 22, by means or the terminal 26, attached to the output strings.

i ducted from the system 22 through the terminal 26, through coil 12(the coil nearer to the strings) and through the return terminal II tofurnish rectified current for magnetically charging the For quietness ofoperation during the charging process, the input terminals I2 and IQ ofthe amplifier are connected together by the switch 30.

By placing the switch 20 in the upward position, terminals 28 and 29 areconnected together, thus supplying rectified current to the amplifier,

and end wire I! of coil I l is connected to the input terminal l8,allowing the device to function as a pick-up structure in accordancewith my invention, coils H and I2 being connected in a seriesarrangement, end wire l4 being permanently attached to end wire l6, asshown.

In Fig. 6 is shown another arrangement. when the singlepole-doublethrowswitch 2| is placed in the upward position, "current is conducted fromthe system 22 through the terminal 28, through coils II and i2, andthrough the return terminal I9 to furnish charging current. By placingthe switch 3| in the downward position the terminals 2G and 29 areconnected together, supplying rectified current to the amplifier andallowing the structure to operate as a pick-up device in associationwith amplifying and reproducing 'means, the coils H and i2 beingconnected in a parallel arrangement, as shown. For simplicity. in Fig.6, as also in Fig. 5, I have omitted. the terminal posts and plate shownin Figs. 2 and 3.

In series with the end wire'in, or Fig. 6, is an adjustable resistance22, which can be used to compensate for any electrical unbalance in theconstruction and assembly of coils II and I2. With the use of theresistance 32 as shown and with the coils I l and I2 in a parallelarrangement it is not necessary that the coils be essentially identical.Coil ll may have more turns and a greater inductance than coil l2; theresistance 22 can be employed to compensate for any lack ofproportionately greater resistance 01' coil Ii, and the device willfunction according to the teachings of my invention.

In Fig. 6 is shown a condenser 22. This serves to isolate the inputsystem of the amplifier from the current of the magnetic chargingprocess.

In both Figs. 5 and 6 are shown a switch 24, which can be used toshort-circuit the output circuit of the amplifier, eliminating any ofthe reproduced noises caused by the operation of the switches 30 and II.Many modifications in the construction of the switches 20, 3| and 24 arepossible, the diagrammatic types shown being merely for clarity ofdescription. One modification that I have found advantageous isoperatively to link the switch I and switch 20 (or ii). Such linkinginsures that the switch 24 be closed preceding the operation of theswitch II (or II) from the pick-upposition to the charsins p sition andthat it be opened after the operation of the switch 20 (or 2!) from thecharging position to the pick-up position.

An additional modification that 1 have found advantageous for quietnessof operation pertains to the switch 30. This switch can be soconstructed that in the operation from the pick-up position to thechargingposition, the following sequence is obtained: first, the inputterminals 18 and it are connected together, then, the end wire I3 isdisconnected from the input terminal l8, and terminals 28 and 29 aredisconnected, and finally, the terminal 26 is connected to coil l2.through the end wire "5. In the operation from the charging to thepick-up position, the reverse of the above sequence occurs.

Many'modifications may be made in structural A features and wiringarrangements and still come within the scope of my invention. What Iclaim as my invention is:

1. In a musical instrument, the combination of a plurality of tunedmagnetized vibratile members arranged substantially in a plane and apick up device for said members, said pick-up device including a framework arranged transverse to said members, a coil of wire on said framework in proximity to said members, a second coil of wire onsaid framework and disposed between said first-mentioned coil and said members,the two said coils being electrically connected in phase opposition.

2. In a musical instrument, the combination of a series of tunedmagnetized strings arranged substantially ina plane and a pick-up devicefor substantially in a plane and a pick-up device for said stringsconsisting of a framework in proximity and transverse to said strings, acoil of wireof substantially planar turns on-said framework in proximityand transverse to said strings, the planes of which turns aresubstantially parallel to the plane of said strings, a second'coil ofwire of substantially planar turns on said framework transverse to saidstrings, the planes of said second turns being substantially parallel tothose of said first turns, said second coll being located between saidfirst coil and said strings, the two said coils being electricallyconnected in phase opposition.

4. In a musical instrument, the combination of a series of tunedvibratile magnetic members arranged substantially in a plane, means formagnetizing said members, and'a pick-up device for said membersincluding a framework arranged transverse to said members, a coil ofwire on said framework in proximity to said members, a second coil ofwire on said framework and disposed between said first-mentioned coiland said members, the two said coils being electrically con- -nectedwhereby said second coil comprises a means for translating the motionsof said members, a coil of wire on said framework in proximity to saidmembers, a core of magnetic material encompassed by said coil, a secondcoil of wire on said framework and disposed between said first-mentionedcoil and said members, a second core of magnetic material encompassed bysaid second coil, the two said coils being electrically connectedwhereby said second coil comprises a means for translating the motionsof said members into electromotive forces and said first coil comprisesa means for neutralizing any stray hum induced in said second coil.

\ ARMAND F. KNOBLAUGH.-

